1. Field of the Present Invention
The present invention is in the field of signal transmission and, more particularly, transmission of power and telemetry signals over a wireline cable.
2. History of Related Art
Wireline cables are used for oil well logging operations in the field of energy related services. Wireline logging refers to lowering instruments at the end of a cable into a well bore. The instruments are designed to take measurements related to the geology and other petroleum related properties of oil wells. Typically, wireline logging includes powering various electrical sensors and actuators by a multi-conductor cable that is commonly referred to as a wireline cable.
Historically, wireline cables have been implemented with six isolated copper connectors helically wound around a center conductor (sometimes referred to as the heptacable). The heptacable cable structure was surrounded by two layers of steel wires. Techniques for transmitting multiple power signals using orthogonal propagation modes over cables of this type have been disclosed. Baird (U.S. Pat. No. 6,469,969), for example, describes a heptacable implementation and a method of transmitting multiple signals over it.
Recent advances in the design of wireline cables have resulted in cables capable of transmitting significantly more power than the conventional heptacable. Wijnberg (U.S. Pat. No. 6,297,455) [hereinafter Wijnberg], for example, describes a wireline cable having four relatively large primary conductors and at least one relatively small secondary conductor. Layered dielectric construction, such as that disclosed by Mydur et al. (U.S. Pat. No. 6,600,108), produces higher voltage ratings without degrading telemetry characteristics. It would be desirable to implement a method and system for transmitting power and telemetry signals over these types of wireline cables that takes advantage of their distinctive characteristics. It would be further desirable if the implemented solution were backwards compatible with conventional wireline cables.